SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.

Chronically high blood pressure is a serious health problem that affects about one out of every three adults and contributes to approximately 17.5 million deaths worldwide each year. While there are many things people can do to try to keep their blood pressure down – lower salt intake, maintain a healthy weight and drink in moderation – studies have shown that genetics also plays a part.

But finding common genetic variations that affect blood pressure hasn’t been easy. Just five months ago The Spittoon reported on the first validated association in Europeans. Now, two large consortia have identified several more. Their findings, published online this week in the journal Nature Genetics, expand the current understanding of how blood pressure is determined and may point the way towards targets for new drugs for treating possibly preventing hypertension.

“None of the genes we identified as having common variation are part of the system we know about that regulates blood pressure – the genes identified are not the ones targeted by current prescription drugs to control hypertension. If we can increase the number of genes implicated in blood pressure maintenance…our understanding of the biology will change completely,” said Aravinda Chakravarti, head of the Center for Complex Disease Genomics in the McKusick-Nathans Institute of Genetic Medicine at Johns Hopkins University School of Medicine and a co-author of one of the studies, in a statement.

The two research groups analyzed data from an enormous number of people – more than 50,000 in the Global BPgen study and more than 29,000 in the CHARGE study. Such large samples are needed because variation in blood pressure is likely due to many variations, each with very small effects.

After conducting their own analyses, the researchers from each consortium shared their findings with each other, allowing the scientists to further confirm their results. All together, six distinct variations associated with systolic blood pressure (SBP) and nine associated with diastolic blood pressure (DBP) were found and confirmed between the two studies. The Global BPgen consortium also studied more than 12,000 South Asian Indians and found evidence for association between blood pressure and two of the SNPs identified in the European studies.

Further analysis of the Global BPgen results showed that all of the SNPs associated with SBP through the genomewide analysis were similarly related to DBP, and vice versa. And not surprisingly, all of the SNPs the researchers identified were also associated with hypertension; the version of each SNP linked to lower blood pressure was also decreased a person’s odds of having the condition.

The effects of the individual SNPs were small, but the authors of both studies point out that small changes in blood pressure can translate to important changes in the risk of heart disease and stroke. For example, the authors of Global BPgen study say that lowering SBP by 2 mmHg has been estimated to translate into 6% lower risk of stroke and 5% lower risk of coronary heart disease. The authors of the CHARGE study cite other data showing that a prolonged increase in DBP of 5 mm Hg is associated with a 34% increase in risk for stroke and a 21% increase in the risk of coronary events.

All SNPs that were found to have significant association with blood pressure by both groups after they shared their data with each other are given below. Those SNPs for which 23andMe can provide data are linked to the Browse Raw Data feature. Some linked SNPs are proxies for the SNPs described in the original articles and are noted as such. The information in the first table applies only to people with European ancestry. The second table provides information on the findings of the Global BPgen study of South Asian Indians.

What does it mean to have “version T” at an SNP? When I click on an SNP in “Browse Raw Data”, I get two letters listed (eg.: CT or GG). To be considered as having “version T” or “version G”, is one T or G enough, or do I need both?

You’re right that your raw data will say something like “CT” or “GG” for a particular SNP. That’s because you get one copy from your mom, and one copy from your dad. Most of the time the studies that we talk about in SNPwatch blog posts will find that each copy of a particular letter at a particular SNP increases or decreases the odds of a condition relative to someone with two copies of the other version. Confusing, I know.

Here’s an example: For rs17367504 (the first SNP in the table in this post), each G decreases SBP by 0.85 mmHg compared to someone with two As. You get more effect for each copy of a G you have. Each G at this SNP also decreases the odds of hypertension by about 11%. So someone whose raw data says AG at this SNP is predicted to have a little bit lower blood pressure than someone with two As, and someone whose data says GG would be predicted to have even lower blood pressure. But of course, this is just one SNP and there are lots of other genetic and environmental factors that have to be taken into account.

Phantom

Thank you for the detailed explanation.

I was unsure because sometimes the blog posts will explicitlysay “each A/C/T/G will have x% effect”, and other times they simply say “version so-and-so will have x% effect.”

I know that sometimes you need to both letters to be the same to have any effect at all, but I guess that in these cases the blog post will clearly specify that.

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